The Hot Zone

Plants are complicated

Posted by Alison Hawkes on August 8, 2010
Category : Climate Science and Scientists

Planting trees, as everyone knows, is a good way to offset climate change. The more greenery on Earth, the better, since vegetation act as carbon sinks, essentially sucking up the excess CO2 and storing it in leaves, stems, and root systems.

But a recent paper published in the journal Nature Geoscience claims we have a long way to go towards understanding the biochemical processes in which plants interact with the climate. Simply looking at the carbon cycle involving plants is not enough, say the researchers led by the earth science department at Lund University in Sweden.

They outlined a number of other biochemical feedbacks worth considering and exploring in greater detail. Take ground level ozone (O3), for example. It’s produced during fossil fuel combustion and causes smog, which is toxic to pretty much all life forms, including plants. Ozone enters through the stomata and effectively destroys a leaf”s ability to produce chlorophyll. The researchers say that O3 toxicity could reduce the global land-carbon sink by 12 to 24 billion metric tons by the year 2100, depending on plant sensitivity.

That’s not all. Consider Nitrogen, that essential soil nutrient that boosts plant growth. Plants generally grow faster under warmer, higher CO2 concentrations in the atmosphere, but only if they have enough Nitrogen to keep them going. “The availability of Nitrogen, which is limited in many ecosystems, plays a critical role in controlling [net primary productivity,” the researchers write.

Although some models suggest that warming will enhance the amount of Nitrogen available to plants in the soil, generally the end result is still higher CO2 levels. No one has incorporated into models of climate feedbacks the impacts of nitrous oxides, which are emitted by microbe decomposition of the soil (and by human activities), despite their extreme potency as a greenhouse gas.

The impacts of biologically produced versions of volatile organic compounds and their generation of cooling aerosols has yet to be incorporated into experiments on how plants change in a warmer planet.

The researchers argue for incorporating more sophisticated models of all these biochemical processes into global warming scenarios. Just looking at CO2 as it relates to plants is not enough.

-Alison Hawkes

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